Modelling the Effect of Surface Roughness on the Localization and Failure Behaviour of AA6111 Sheet

Localization and failure of sheet metals are known to be sensitive to the presence of surface asperities. In this thesis, characteristic frequencies and amplitudes of surface roughness have been obtained from undeformed and deformed AA6111. These measures are then incorporated into two-dimensional finite element method (FEM) models to study the relationship between surface roughness and microstructural damage in sheet forming failures. The FEM models are capable of simulating the coupled effect of shear bands and voids on sheet localization behaviour by employing a mixed isotropic/kinematic hardening form of the Gurson-Tvergaard-Needleman (GTN) constitutive softening equations. The effect of the relative positions of top and bottom surface defects was studied using three different model geometries.

The FEM models predict that the defect amplitude plays a strong role in causing earlier onset of localization and failure. Furthermore, the relative positions of defects on the top and bottom surfaces plays a significant role in the determination of failure mode, specifically necking failure versus through-thickness macroscopic shear banding. The FEM models also show that, under certain geometric conditions (i.e. the combination of defect amplitude, wavelength, and phase), macroscopic shea banding can cause failure at lower values of strain than necking.

Year	Entry
2001	Lievers WB. Effect of Void Damage and Shear Band Development on the Bendability of AA6111 Automotive Aluminum Alloy Sheet [Master's thesis]. Ottawa, ON: Carleton University; May 9, 2001.
1982	Triantafyllidis N, Needleman A, Tvergaard V. On the development of shear bands in pure bending. Int J Solids Struct. 1982;18(2):121-138.
2004	Lievers WB, Pilkey AK, Lloyd DJ. Using incremental forming to calibrate a void nucleation model for automotive aluminum sheet alloys. Acta Mater. June 7, 2004;52(10):3001-3007.
1979	Goods SH, Brown LM. The nucleation of cavities by plastic deformation. Acta Metall. 1979;27(1):1-15.
1975	Gurson AL. Plastic Flow and Fracture Behavior of Ductile Materials Incorporating Void Nucleation, Growth, and Interaction [PhD thesis]. Providence, RI: Brown University; June 1975.
1984	Tvergaard V, Needleman A. Analysis of the cup-cone fracture in a round tensile bar. Acta Metall. 1984;32(1):157-169.
1977	Gurson AL. Continuum theory of ductile rupture by void nucleation and growth, I: yield criteria and flow rules for porous ductile media. J Eng Mater Technol. 1977;99(1):2-15.
1983	Brownrigg A, Spitzig WA, Richmond O, Teirlinck D, Embury JD. The influence of hydrostatic pressure on the flow stress and ductility of a spherodized 1045 steel. Acta Metall. August 1983;31(8):1141-1150.
2003	Lievers WB, Pilkey AK, Worswick MJ. The co-operative role of voids and shear bands in strain localization during bending. Mech Mater. July 2003;35(7):661-674.
1980	Chu CC, Needleman A. Void nucleation effects in biaxially stretched sheets. J Eng Mater Technol. 1980;102(3):249-256.
1987	Tvergaard V. Ductile shear fracture at the surface of a bent specimen. Mech Mater. 1987;6(1):53-69.

Year

Entry

2001

Lievers WB. Effect of Void Damage and Shear Band Development on the Bendability of AA6111 Automotive Aluminum Alloy Sheet [Master's thesis]. Ottawa, ON: Carleton University; May 9, 2001.

1982

Triantafyllidis N, Needleman A, Tvergaard V. On the development of shear bands in pure bending. Int J Solids Struct. 1982;18(2):121-138.

2004

Lievers WB, Pilkey AK, Lloyd DJ. Using incremental forming to calibrate a void nucleation model for automotive aluminum sheet alloys. Acta Mater. June 7, 2004;52(10):3001-3007.

1979

Goods SH, Brown LM. The nucleation of cavities by plastic deformation. Acta Metall. 1979;27(1):1-15.

1975

Gurson AL. Plastic Flow and Fracture Behavior of Ductile Materials Incorporating Void Nucleation, Growth, and Interaction [PhD thesis]. Providence, RI: Brown University; June 1975.